Automatic constant speed governor for engines driving variable pitch propellers



Feb. 16, 1954 s ms 2,669,310

AUTOMATIC CONSTANT SPEED GOVERNOR FOR ENGINES DRIVING VARIABLE PITCH PROPELLERS 2 Sheets-Sheet 1 Filed May 17, 1950 ENGINE 0 TAOHOMETER PAD ATTORNEY? SPEED ERROR w w m mmR m W. 5 W mm mm M w WWW mm R M NEH i m A m Rmm mm H a 0 mm T 0 b m 5 ll Lm 5 1 w m w w w EE E 2 3 Ir I I J)? Z OUUQW wmv finm m ll Tl Feb. 16, 1954 R. HASKINS 2,669,310 AUTOMATIC CONSTANT SPEED GOVERNOR FOR ENGINES DRIVING VARIABLE PITCH PROPELLERS Filed May 17, 1950 2 Sheets-Sheet 2 INVENTORI ROBERT HAS/(INS 5 A BY g a ATTORNEY)? Patented Feb. 16, 1954 AUTOMATIC CONSTAN FOR ENGINES DRIVI PROPELLERS I T SPEED GOVERNOR NG VARIABLE PITCH Robert Haskins, Richmond, Va.,.assignor to Flight Research, Inc., .acorporation of Virginia Application May 17, 1950', Serial No. 162,475

11 Claims.-

This invention relates to automaticv control systems, and particularly to automatic constant speed governors for aircraft engines.

It has long been known to obtain substantially constant speed control of an aircraft engine by varying the pitch of the propeller driven by the engine in response to en ine speed changes, so that the resulting change in pitch causes the speed change to be corrected. Such devices have included those of the hydraulic type, which have been extremely costly.- Where automatic constant speed governors involving speed responsive control devices employed to control an electric pitch changing motor have been suggested, the results have usually been unsatisfactory because ofthedelicate and-relatively undependable nature of the electrical control systems employed.

In contrast to such prior devices, the present invention provides-an automatic aircraft engine speed control system of the type wherein speed changes of the aircraft engine are translated into corrective adjustments of the pitch' of the air.- craft" propeller by means of an eddy current type speed sensor driven from the aircraft engine, a photoelectric system activated in response to ac tio'ns of the speed sensor, and a pair of control relays selectively actuated by the photoelectric system in accordance with the-actions of the speed sensor; thecontrol relays operating to en ergize selectively the increase and decrease Windings-of'a conventional electrical pitch changing motor carried by the propeller.

The-invention further provides a novel arrangement for obtaining, with a simple speed responsive photoelectric control system, contrclling-actions which are substantially proportional ts the true'speed change or error, so as'to avoid any-material tendency of thecontrol system to hunt.

In'a preferred form, the invention includes an eddycurrent type-speed sensor driven from the ai"cra'ft' engine and serving to translate engine speed changes into torque applied toa rotatable drag cup, a light vane moved by the drag cup,

a manually adjustable spiral spring biasing device arranged to appl a positioning or restraining force to the drag cup, a light source, a pair of photoelectric cells arranged to be activated by the light source, the light vane being positioned tdnormally prevent the passage of light from the source to either photoelectric cell but being laterallydisplaced as aresult of rotation of the drag cupto allow selective activation of the photoelectric cells, and electrical means for -selectivelyactuati-ng, in response to action-of the 9 bl photoelectric cells the respective powerrelays controlling the increase and decrease windings of the electrical pitchchanging motor. Thus, the.

vane, and therefore the controlling operation of the device as a whole, at any one instant depends upon the resultant-efiect upon the drag cup of the speed sensor. and-the manually adjusted biasing device, so that a major feature of the invention isthe provision in such a device of means by which the engine. speed maintained by the device can beselected manually.

In a preferred form, the invention also pro-- vides means for returning the light vane to its normal position Whenever one of the photoelectric cells is activated, the returning means being op-. erable only while a cell is energized and having a returning power suflicientto center the. light vane, overcoming the-action of thespeedsensor, only if thevane is notdisplaced more than .a predetermined amount. If the speed error is large, then theireturning means, though actuated, is ineffective." Thus, the controlling-action of the device is continuous for relatively large speed errors, but is cyclically interruptedto give proportional control w-henever the speed error is relatively small.

Another important feature ofthe invention-is the provisionzof means whereby short circuits-or other electrical failures of the deviceresultin substantially instantaneous termination. ofthe control-action, so that the pitch of the propeller hereafter remains as it was the moment the failure occurred.

In order that *theseand other features of the invention may'be readily understood, reference ishad to the-accompanying drawings, which-form apart of this specification, andwherein:

Figure l is a diagrammatic-illustration of one embodiment of the invention;

Figure 2 is a diagram illustrating the operation of aninterrupter magnet employed in the invention for. obtainingsubstantially proportional control action;

Figure 3 is a schematic diagram oia preferred circuit forming a part of the invention and operating to obtain actuation of a pair of motor control relays in response to selectiveactivation of a pair of photoelectric cells;

Figure 4 is a partial plan view of the mechanical organization of the speed sensing mechanism and speed selecting means employed in the invention;

Figure 5 is a sectional view 5--5," Fig. 4;

taken on the line Figure 5- is a vertical sectional view of a preferred eddy current speed sensor and drag cup mechanism employed in the invention;

Figure 6 is a fragmentary plan view of a portion of the speed selecting means of the inven tion, and

Figure '7 is a plan view of the drag cup and associated elements employed in the invention to translate detected engine speed error into selective operation of a photoelectric control system.

Fig. 1 illustrates diagrammatically the general combination of elements employed in a preferred form of the invention. Here. it will be seen that an eddy current type speed sensor S is driven by a flexible shaft Hi rotated from the tachometer pad ll of the aircraft engine. The speed sensor S serves to angularly position a drag cup !2 in response to engine speed change, in a manner well known in the prior art. The drag cup i2 is supported by a rotatable shaft 53 biased against rotation by a pair of spiral hair springs M and 55, as hereinafter described in detail. The restraining springs I4 and i5 are connected at their centers to diametrically opposed points on the shaft I3, and at their outer ends to a speed range adjusting gear 56. A pinion i1, rotatable through a flexible shaft it! manually turned by knolo is on the aircraft instrument panel, meshes with the gear l5. Thus, the angular position of. the drag cup I2 is determined by the resultant of the force applied thereon by the speed sensor and the restraining force applied to th shaft by the hair springs.

The drag cup 12 carries an opaque light vane 20 and, diametrically opposed thereto, counterbalance 2|. The light vane 20 is positioned between a light source 22, such as an incandescent lamp energized from any suitable current source. and a pair of spaced photoelectric cells 23 and 25. in such a manner that, when th drag cup i2 is in a predetermined centered or on speed position, no light from the source is allowed to fall on either photoelectric cell. while material rotation of the drag cup in either direction will. e2:- pose one or the other from the light source. It will be clear from the foregoing that the centered position of the drag cup is determined by the position of the range adjusting knob l9, and that activation of either of the two photocells results only from a material engine speed change as translated by the speed sensor S into lateral displacement of the light vane 20 to the right or left, depending upon the sense of the speed change.

The photoelectric cells able relay actuating circuit, here indicated at to actuate selectively a pair of control relays 2G and 21. Through control circuits to be described, the relay 26 controls a power relay 126 which serves when deenergized to interrupt the supply circuit for the increase winding 1 of the propeller pitch changing motor indicated schematically at M, and the relay 2'! controls a second power relay 121 arranged when deenergized to interrupt the supply circuit for the decrease winding d of the pitch changing motor. The winding 1' is supplied from a suitable power source through the conductor I33, while the winding :1 is supplied from the power source through conductor we. The actuating winding of power relay 26 is supplied from a suitable power source by conductors i322 and I28, the circuit being completed to ground via conductor I29, while the actuating winding of the power relay? is similarly supplied from the of the two tubes to light 23 and 2 control a suiti biasing force of the springs M and 4 same source by a circuit comprising conductors 132,!39 and 13!.

Bridged across the conductors M3 and I30 is the series combination of two resistances 32 and 33, and the junction between the two resistances is connected to conductor 36 leading to the winding of an electromagnet 35 and thence to ground. Carried by the counterbalance 2! is a magnetic element 35, such as a soft iron slug, and the electromagnet 35 is positioned on a vertical line with the magnetic element 34 when the drag cup I2 is in centered position. Whenever one of the control relays 2% and 2? is energized, current will flow through the corresponding one of the resistances 32 and 33, conductor 38, the winding of electromagnet 35, and to the grounded side of the power relay supply. Thus, energization of either of the relays 25 and 2? results in simultaneous energization of the electromagnet 35. The electromagnet 35 will then attract the magnetic element 34;

The relay actuating circuit 25 is supplied from a suitable current source, which may be the same source employed to energize the power relay windings, by a circuit comprising conductor 38 and ground. A manual switch 39, located on the aircraft instrument panel, is provided to make and break the supply to the circuit 25, as shown. The manual switch 39 is preferably a 3-position switch, the remaining two contacts thereof being employed for selective manual control of the power relays l26 and I21 via the conductors l36 and 131, respectively, as shown. Thus, the switch 39 can be used either to activate the relay actuating circuit 25, or to selectively energize either power relay to the exclusion oi the automatic control.

Operation of the device illustrated in Fig. l is as follows: Assume that the springs l4 and I5 apply a given biasing force to the shaft l3, and that the aircraft engine R. P. M. driving the speed sensor S is insufficient to equalize the biasing force of the spring. Assume that relay actuating circuit 2:: is so designed that activation of photoelectric cell 24 actuates the relay circuit to energize relay 2? and thus energize the decrease winding of the propeller pitch adjusting motor. The effect of the speed sensor S upon the drag cup 12 being insufiicient to equalize the :5, the drag cup is angularly displaced in a direction causing the vane 2% to allow light from the source 22 to impinge upon the photocell 2c. The photocell 24 is thus activated, controlling the circuit 25 to energize the relay 21, causing the circuit to the decrease winding of the pitch changing motor to be completed, and so energizing the motor to decrease the pitch of the propeller and thereby causing an increase in R. P. M. of the aircraft 7 engine, which speed increase is translated by the speed sensor S into a corrective change of force upon the drag cup i2. If the relay 2'! were to remain energized until the propeller pitch had decreased sufiiciently to result in a speecl increase of such magnitude that the drag cup 12 and its associated light vane 29 were returned to centered position, it is obvious that severe hunting would result, due to the time lags resulting from the inertia of the engine. Accordingly, some means for approximating proportionate control, instead of employing the simple on-ofi control just described, must be provided. This is accomplished by the electromagnet 3'5.

Upon energization of the relay 2'], current flows through the resistance 33, and the electromagoperation is toasupplyr-a' short fpulse of current toj the decrease winding .ofzthe pitchchanging "motor.

The vane and cup assembly, :biased I by "the -springs Mand lLi-has a :natural period deter- -=mined by-the moment. of inertia of :cup assembly :and the stiffness of the springs. The -assembly is so designed :"that the "torque produced by" the interrupter magnet I35 causes :the =vane :to return relatively slowly to centered position. 'Inaaetual practice, Ihave'found'that "-forroptimum performance, the natural period r of -thevane and cup-assembly should be -in the range 5-15 seconds. The natu-ral'periodof the vane .and cup assembly of coursedetermines the durationro'f the. pulse-of changing-motor. Ifithe natural period is:substantially below .5 second, thecurrent pulsemay be soshort that the pitch motor cannotproperly acceleratethemotor will be :unable to :attain sufiicient speed, and severe arcing-of the :relay contacts will result. If the xnatural period 'is toolong, the corrective pulse o'fcurrent applied to the pitch motorwill be of z'suchilongduration that an overshoot will occur,

".whichiwill resultin oscillation or'hunting of the 1 entire system.

When-the relay-r21 opens as a result oicentering:o'f*the:drag cup-and light vane by-the-action of the electr01nagnet 3l5,--

longer flows through resistance -33. With the electromagnet 35 deenergized, the-drag cup 12 andits vane 28 .are free to :return to whatever angular position is determined *by :the existing resultant of the forces-applied to :the dragcup by the springs "I 6 and 1'5 and the speed sensorS. "There ore, if athe engine speed, as it affects the speed sensor, it still insufficient to counterbalance the biasing forcesofthespringazthe from-the souroe iito fall upon the photoelectric cells, and another pulse of current will "be supplied-to the decrease =.vinding of the pitch changing-motor in the same manner as just described. Thisactionvv'illcoiitinueuntil the pr0- :peller pitch has been changed-sufficientlyto result iinz-an engine speed.- change of proper magnitude to cause the speed sensor to counterbalt-ance the torque of "the "biasing springs. Upon :the end of the last pulse-of current to the de- 23-will be activated, and relay 26 will 'serveto energize theincreasewvindingof the'p'itch changing motor.

In the foregoing explanation it'has been assumed that the i'nitial difference between the forces M: and. [Sp-thus causing the the vane and current applied tothe pitch exerted upon the drag cup by the speed speed change translated "error is small; and increases creases. Obviously, "ofrelativelylarge value, depending upon the de- "signo'f 'electromagnet -35, the initial deflection of sensor *endthe biasing lsprings zis ssuffieiently small .that :when the electromagnet '1'3'5 is energized upon actuation of one of the relays 26;:and 27, the power of the electromagnet will. be. sufiioientlto cause-.the dragcup to be centered. But, the initial resultant :force .upon the drag :cup

tmaycobviously be soxgreat that the-drag .cupwlll be rotated 'sufii'ciently to efiectively remove the magnetic element 34 ifromatheifield of the electromagnet 35. When this is :true, rthe electromagnet will initially be unable to :return .the

drag cup'to centered position, eventhoug'hzthe .electromagnet is of course energizedsassoon as one of therelays 26 and?! closes. But, .as:.the propeller pitch isehanged,v resulting in an engine into a changeof: force on .thedrag'cup by the speed sensorisytheldrag cup willigradually move toward centered'zpositionpand the magnetic element therefore .is graduallymovedzback into .thefield of the electromagnet 35. Therefore, asthe engine speed error, as represented bythe difference inz-eife'cts 'ofithe'springs 1'4 and land thespeed sensorr-S, approaches zero, the electromagnet 35 Willagain come into effective operation. The deflection required to removethe magnetic element from ftherfield of therelectromagnetT35 can obviously bepredetermined by. proper design of. the electromagnet.

The operation of of the-device. "This ratio in turn depends upon the magnitude of the 'speed error. shown bytheicurve of Fig. '2, the average speed "is low When thespeed asthe speed error infor some given "speed :error value, the pitchchanging motor is operated con- 'tinuously'untilthe speed error is'reduced by'the governor to a value sufiicientl-y 81113.11 that the magnetic element il-t -again comes within the ef- "fective field of the 'electromagnet 35. As the speed error is further reduced, the operation of the =electrornagnet '35, cyclically returningthe vane 26 to centered position, progressively reerror, the greater is the deflection of the drag cup, and the-greater the "distance between the electromagnet 35 and the magnetic elenient 34 at the start of thecentrol action. "Thus-since the 'force of attraction of the electromagnet for the stood that this need trol the grids of a the plates of the tube being connected to the actuductor t i a multiple connector 42 to the manual switch 39 stationary contact 55 21. The supply conductor winding proportional to speed While the preferred embodiment of the invenx.tion provides for a restoring force which is a function of the speed error, it should be undernot beso for satisfactory operation. If desired, the electromagnet 35 can be so designed as to restore the drag cup 12 from any deflected position.

Fig. 3 shows in detail a preferred electrical circuit for use in the device described with reference to Fig. 1. Here, the photoelectric cells 23 and 24, selectively activated by light from lamp 22 by reason of the action of light vane 25, condouble beam amplifier tube to,

ating coils of the increase relay 2%} and the decrease relay 21, respectively, and thence to con- The conductor 4| is connected through on the aircraft instrument panel, by which switch the circuit is connected to a suitable source of current.

The photoelectric cells 23 and 2d are connected to conductor 5% and, through suitable resistances 53 and id, respectively, to grounded conductor 35. The lamp 22 is connected between conductor 5,! and ground.

The movable contact 55 of relay 25 is biased in any suitable manner to engage a stationary contact 131 when the relay is deenergized, and is brought into engagement with a stationary contact when the relay is energized. The movable contact 29 of the relay 21 is biased to engage a when the relay is deenergized, and is brought into engagement with a stationary contact 55 when the relay is energized. The stationary contact 51 is connected by the conductor 5! to one terminal of the actuating winding 52 of a safety relay 53, the remaining terminal of winding 52 being connected to ground. By a conductor 56, the stationary contact 41 is also connected to the movable contact of relay 5! is connected by the conductor 55 to the movable contact 45 of the relay 25, and thence by a conductor 55 to the stationary contact 55- of the relay 21. The stationary contact =18 or" the control relay 25 is connected by a conductor 51 through the normally open contacts of the safety relay 53 to the multiple connector c2 and thence to the actuating (not shown) of the power relayior the increase winding of the pitch changingmotor. The stationary contact 5! is connected by a conductor 58 through the multiple connector 42 to the actuating winding (not shown) of the power relay for the decrease winding of the propeller pitch changing motor. Bridged across the conductors 51 and 53 is the .series combination of resistances 32 and 33, and the junction between these two resistances is connected to one terminal of the winding of the interrupter electromagnet 35, the remaining terminal of the winding being connected to ground.

When the photoelectric cell 23 is activated by light from the lamp 22, the cell becomes conductive and thus applies a potential to the corresponding grid of the tube as, which thereupon becomes conductive as to the plate connected to the winding of relay 2%. The relay 26 is thus energized, causing its movable contact 45 to engage the contact at. A circuit is thus completed from the conductor cl, through the conductors 55 and 51 to the multipie connector 62, and thence to the power relayfor theincrease winding of the pitch: changing'motor. --The relay 21 being deenergized, current flows through the conductor 56, the contacts 49 and 50, and the conductors 54, 5| to energize the winding 52, causing the safety relay 53 to complete the circuit through the conductor 51. Since the relays 25 and 53 are energized, the interrupter electromagnet 35 'is energized by current flowing through the conductor 35 and the resistance 32, and as described with reference to Fig. 1, the interrupter magnet serves to cut on the flow of light to the photoelectric cell 23. Upon deactivation of the cell 23, the tube 453 becomes non-conductive as to the plate connected to the relay 26, and this relay is accordingly deenergized. the contact 45 thereof returning to engagement with stationary contact 41. Supply of current to the power relay of the increase winding of the pitch changing motor is thus interrupted. Simultaneously with deenergization of the relay 25, the interrupter electromagnet 35 is deenergized, since current no longer flows in the resistance 32.

When the photoelectric cell 24 is activated by light from the lamp 22, the tube 40 is made conductive as to the plate connected to the winding of the relay 21. This relay being thus energized, the movable contact 49 is brought into engagement with the contact 5|, completing a circuit from the conductor 5! through the conductor 55, the contacts t5 and 41 of relay 26, the contacts i9 and 51 of relay 21, the conductor 58 and, through the multiple connector 42, to the power relay for the decrease winding of the propeller pitch changing motor. Upon energization of the relay 21, current flows to the interrupter magnet 35, the vane 25 is therefore moved to cause the photoelectric cell 24 to be deactivated, and the relay 21 is thus deenergized.

It is clear that, so long as a sufiicient speed error of either sense exists, the cycle of operation of the circuit shown in Fig. 3 will be repeated, as previously explained in the description of Fig. '1.

When there exists an engine speed error such as to cause the speed sensor to allow light from the source 22 to activate the photoelectric cell 23 and thus cause the relay 25 to be energized, the increase winding of the pitch changing motor will be energized, providing that the contacts of relay 21 are in deenergized position so that safety relay 53 in energized to complete the conductor 51. When there is an engine speed error such as to cause the speed sensor to allow light from the source 22 to activate the photoelectric cell 24 and thus cause-the relay 21 to be energized, the decreasewinding of the pitch changing-motor will be energized, providing that the contacts of the relay 25 are in deenergized position so that from the conductor 55 to the conductor 58. Should there occur in the circuit of Fig. 3 a short circuit such as to cause therelay 21 to be continuously energized so that current flows continuously in the conductor 58, the decrease winding of the pitch changing motor is then energized, the propeller pitch is therefore decreased, and the engine speed falls off. Accordingly, there is a speed error such as to cause the speed sensor to allow light to fall upon the photoelectric cell 23, and the relay 25 is energized. Both the relay 26 and the relay 21 now being energized, no current can flow to the winding 52 of the safety relay 5%, and the conductor 51 is accordingly interrupted to prevent energization of the increase winding of the pitch changing motor. And, sincethe re1ay26 is energized, current cannot? now -flow "from theconductor 5 5 to the" conductor 58. Thereifectof the short'circuitithus:

isto causeinofu'rther 'en'ergizationof either wind ingl 01': the pitch? changing motor," and I th peller r pitch remains- -substantiallyI as it the: time I the short circuit I eratori: can then operate e proo'ocurr'edb The 1. the selector switch 39',

Fig.- l, vto." deac-tlvate'r'the automaticcont1o1 and 1 change over to manualcontrol ofthe f power-"re lays oi' 'th'e' pitch changin We'll-known before th'e present invention.

Should a short'oircuit: 0c relayi 26* to be continuously" energized, the increase windin'giofthepit being: energized, the saf gizedxbreaking.the conductor 51 and 50 causing theiincrease winding of the pitch changingmotor to be deen'ergized'. And, andztlthe relayil'l are en flow-'froinlconductor' theideoreasewmding.

ergized, current cannot of I the pitch changing motor I is deener'gizeda Again, the pitch of the propeller remainssubstantially as :it was: when the short circuitzoccurred', and the-"selector: switch 39,-.Fig;- 1,- t can he r-actuated I to deactivatethe automatic control 'and cha'nge over to manual control.

It 'will b'e noted from: Fig. '3 that, when'-a short anually adjustable biasing a" lower: bearing plate 63.

Located above the'-'plate": 63 is an upper i bearing:

p1ate-s64',- =.supported by. suitable uprights; one of whichisashown at 65; Fig;

6 I .and- 62 :re'spectively; 68 ,"wh'ich.-.plate has a lamp-J 22 -;is carried :by": a suitable conventionalsocket'--,18-mounted on:the paneI iBU in a position ocatedbelow the opening The photoelectric cells 23 such; that. ithe lamp, is l 6910f the plate: I 68; and-#Zk-are located one ateach side -oftheopening-nBS, the-cells 'bein manner on the platefifl the details of themount ing: depending vuponathe nature of the cells em-- played." Fortsimplicity, only photoelectric cell- 24 'has been-illustrated, and it will be understood that the c ametrically across :the open-ingeBQ I from the-cell Mt- Th'e vertical shaft -I3-of the drag cup; I2 --extends upwardly ithroughthe lower 63and, abovetheplate :63,- ends of f the spiral sprin in -Fig; 4-and more "clearly: dr'agzcupzl ZIisthus supported immediately above the speed sensor S, and the light vane 2B-'car= riedi- -by tne=drag cup extends horizontally under the plalte 68 so as to beinterposed-betwen the is secured to the inner was at g; motor; Y in a manner cur which causesthe .since both the'relay 26' '55 to the conductor 58, and

the speed-sensor; drag 1 cupr magnet, I light source and d spaced, upright supports vethepaneltfl byithesup- 5i A pai-r of horizontal :arms :66': and-.161; .mounted" on the uprights support a horizontal plate I central opening 69." The" g." mounted in any suitableell 23 is similarly mounted -di-" bearing plate gs I4 and- I5, fas seen: shown inFigi 6: The r cally upward between -th Ianip 'ZZ'and the'aperture' 59. Asseen in'Fig 4; a vertical light partition 1! ismounte'd onthe uppersurface of the-plate 68 and extends ve'rth ephotoelectrie cells 23" and 25. Thus, if thev'ane 2G is displaced lateial- 1y sufficientl y 'to-allow light fronr lamp 22 to fall-'upon the cell 24,-the' p' tition li prevents anyofthe lih't from reaching the cell 23. In like-manner; the partition -'5 5 serves to maintai-n"the cell 24dactiva'ted whenthe light vane is disp'laoed in "-the' opposite direction to activate eel-123; Thevan'e 2il is-provided withside exten sions 'll and fate-engage 'a central stop 'ldjcari'ieei bythe p121 12 68; The interrupter magnet 35 is -su'pp'ortedby' a bracket i5 carried i23 and extending: horizontally above the c'en-" tel-ed position of magnetic element 34":

" illustrates in detail one manner in Which thedrag. cup 'sha'i may beniountedc Here; it is seen "tha t the speed senson-iwhile the upper support for 'bhe shait is a bea-ringzilz selector gear- I 6 lies" upper surface of the shownin Fig. 6, is provideding: materially" larger: than st-ructure; so that the spee be supported for free-rot bushing 36, the bushing 76 bein the drag. cup shaft structure. speed selector is are support ingv plate" 53-, each other; I4 "and I5.

The spiral restrainin inclosely: spaced paral speed selector gear I 6.- spiral spring is connect the 'drag cup shaft;- the"- dselector gearmay" g spaced from ed for free rotation by the'bar but are 'free'to rotate "relative to except for' the-restraining springs lel planes just "above 'th'e The innerend of each ed to a hub carried by points of connectionof the'two springs being diametrically opposed as uter end of spring I 4" is xtending Jupw'ardly from shown in-F'ig; -6.' The 0 connected 'to apost 7 1 '-e gear: I 6;.and the outer connectedto: a similar: 6;.the posts "l'l and-78' across 1 thegear I 6; a them would intersect tween the points of end ofthe spring I5 isconnection of the inner ends-of the twosprings I4-and I5. It will thus raining forces applied to r and I5-dependbe seen I thatthe rest the shaft I 3 by thesprings I4 upon the angular position of-th Further, therestrainin by the two springs areT additive; to the shaft at diametrically oppo restraining action of the adjustablespring means therefore :has no tendency to displace the shaft I3 sidewise. This-is-a-feature important to sat isfactory operation of the control device as ae speed selector g-iorces applied-- but are appliedsed points.

journalled inthe-bearingplates 63-and -64 and-- provided at its upper end with a spline connection adapted==to re shaft -IB, Fig. 1, so th shaft- I 8 results 'in rot suming (that the speed to the drag 'icupfl ceivethe end of flexible ation' of the-gear" I62 As I 2, then clockwise rotation of 1 by the lower bearing plate and-speed-selectorgear in theplate 63: Thespeed immediately adjacent the bearing-plate 63 and, as with a central open: the dragcu'p' shaft ation' by an" annular Thus; botlr the gear I6 and the-drag cup shaft 1 g springs 1 I4 are locatedarediametrically.-opposed nd a line drawn between at'right angles a line heat manual 'rotation' of thesensor-S- applied'no forcemanual speed selector knob l9, Fig. 1, would, through the pinion H, the gear is and the spiral hair springs l4 and I5, produce a clockwise rotation of the drag cup shaft 13. With the speed sensor applying a counterclockwise torque to the drag cup, it is then clear that the position assumed by the drag cup is determined by the resultant of the forces applied to the drag cup by the speed sensor and the two restraining springs. The device thus functions to compare the engine speed, as detected by the speed sensor, with the setting of the manually adjusted speed selecting means comprising shaft is, gears l1 and I6, and springs Hi and I5, and to translate any existing speed error into selective activation of the photoelectric cells 23 and 24, the particular cell activated depending upon the sense or direction of the speed error.

Fig. '7 shows in detail the combination of the drag cup [2, the light vane 29, th counterbalance 2i and the magnetic element 34. The counterbalance 2| of course-serves only to ofiset the unbalance in the rotating system caused by the presence or" vane 23, and its function could be accomplished entirely by making the magnetic element 3% of proper weight. But, in order to obtain a sharper action of the interrupter magnet, it is desirable that the magnetic element 3d have a small dimension in the direction of rotation of the drag cup. element 34 is made rectangular in shape, positioned with its longer dimention radial to the drag cup, and is kept small relative to the total mass of the counterbalance.

I claim:

1. In a speed responsive control mechanism, a pair of electro-responsive control devices; a pair of light-responsive devices; light means for activating said light-responsive devices; electrical means for energizing said control devices selectively in response to activation of said lightresponsive devices; an eddy-current type speed sensor including a rotatable drag cup and means biasing said drag cup against rotation, said speed sensor operating to rotate said drag cup selectively in either direction from its initial position in response to speed changes of the device controlled; a light vane arranged to be moved by rotation of said drag cup, said light vane being positioned to control the flow of light between said light means and said light-responsive devices; a magnetic element carried by said drag cup at a point radially removed from the center thereof; an electromagnet arranged adjacent the initial position of said means for energizing said electromagnet to attract said magnetic element only'when one of said electro-responsive control gized.

2. In an automatic constant speed governor for an engine driving a controllable pitch propeller, an electrical propeller pitch changing motor having a pitch increase winding and a pitch decrease Winding; a first circuit for energizing said increase winding; a first normally deenergized control relay, said relay being arranged to complete said first circuit only when said relay is energized; a second circuit for energizing said decrease winding; a second normally deenergized control relay, said relay being arranged to com- Accordingly, the

magnetic element, and g devices is enerplete said second circuit only when said second relay is energized; a movable control element; engine speed responsive means for applying a positioning force to said control element, the

ma nitude of said positioning force being pro- 12 portional to true engine speed; manually ad justable means said control element in opposition 'to said positioning force and proportional to desired engine speed; electrical means responsive to the position of said control element for energizing only said first relay when said positioning force predominates and for energizing only said second relay when said biasing force predominates, and electrical safety means for preventing completion of both of said control either of said circuits when relays are simultaneously energized, saidsafety means including open contacts in one of said circuits, and energizing means for said safety relay including con- 1 tact means opened whenever the control relay for the other of said circuits is energized.

3. In an automatic constant speed governor for an engine driving a controllable pitch propeller, an electrical propeller pitch changing motor. having a pitch increase winding and a pitch decrease winding;

energizing said increase winding; a first normally deenergized power relay arranged to complete said first power circuit only when saidv first power relay is energized; a first normally deenergized control relay; completed only upon energization of said first control relay for energizing said first power re-'-.

lay; a second power circuit for energizing said decrease winding; a second normally deenergized power relay arranged to complete said second power circuit only when said second power relay is energized; a second normally deenergized control relay; a second control circuit completed only upon energization of said second control re lay for energizing said second power relay; means for energizing said first control relay in response to excessive engine speed and for energizing said second relay in response to insufficient engine speed; a safety relay having normally open contacts in said first control circuit and being arranged to complete said control circuit only when said safety relay is energized, and means energizing said safety relay only when said second control relay is deenergized.

4. In a speed responsive control system, the combination of a pair of control relays, a pair a of photoelectric cells, light means, electrical means for selectively actuating said relays in re sponse to activation of said photoelectric cells by light from said light means, a rotatable control element, a light vane carried by said cont'rol'element and interposed between said light means said control element in one direction moving said vane to allow light and said cells, rotation of to impinge upon one of said cells and rotation of said control element in the other of said cells, means responsive to the speed of the controlled device for applyingto said control element a deflecting torque proportional to the speed of the controlled device, biasing means for applying to said control element 5 to said deflecting centered position is less than a amount.

5. In a speed responsive control system, the a pair; of

combination of a pair of cpntrolrelays,

for applying a biasing force to.

a safety relay having normally a first power circuit for.

a first control circuit the opposite direction moving said vane to allow light to impinge upon centered position, in

to either of said cells, when the deviation of said control element from predetermined goo s-1:0:

moving said vane to allow light to impinge upon the other of said cells, deflecting means responsive'tothe speed of the controlled device for applying tosaid control element a deflecting torque proportional to the speed of the controlled device,=.biasing means for applying to said control elementa biasing torque in opposition to said deflecting torque, electromagnetic means for applying a restoring force to said control element, andanelectric circuitfor energizing said electromagnetic means only when one of said relays is actuated.

6. In a speed responsive control system, the combination of a pair of electro-responsive control devices, a control element, a shaft mounting said control element for rotary movement in a single plane, deflecting means operated by the device controlled for app-lying to said control element adefl'ecting torque proportional to the speed of the device controlled, a bias adjusting member mounted for free rotation about said shaft in a plane parallel to the plane of movement of said control element, a spiral hairspring connected at its. center to said shaft and at its outer end to saidbias adjusting member, manually operable means-for adjusting the rotary po ition of said bias adjusting member to apply a biasing torque to saidicontrol element in opposi n to said deflectingtorque, an actuating circuit controlled by said control element and operativel connected tosaidf control devices to energize one of said control'devices when said deflecting torque predominates and the other or" said control devices When said biasing torque predominates, a magnetic element carried by said control element at a point radially removed from the center thereof, a single electromagnet, means mounting said electromagnet entirely outside or" the path of movement of said control element and substantially aligned with the position occupied by said magnetic element When said biasing torque and said deflecting torque are equal, and an electrical circuit arranged to energize said electromagnet to attract said magnetic element only whenever either of said control devices is energized.

7. In a speed responsive control system, the combination of a pair of electro-responsive control devices, an eddy-current speed sensor including' a rotatable drag cup and means driven by the controlled device for applying to said drag cup a deflecting torque proportional to the speed of the controlled device, biasing mean operatively connected to said drag cup to apply thereto a biasing torque in opposition to said deflecting torque, means responsive to the position of said drag cup for energizing one of said control devices when said deflecting torque predominates and the other of said control devices when said biasing torque predominates, a magnetic element carried by said drag cup at a point radially removed from the center thereof, a single electromagnet, means mounting said electromagnet entirely outside the path of movement of said drag cup and substantially aligned with the position occupied by said magnetic element when said said light means.

torques are equal sothat rotation of said drag cup resulting from predominance of either of said torques tends to remove said magnetic element from the field of said electromagnet and the attraction of said electromagnet for said mag,-

netic element is thus inversely proportional to, the diflerence between said torquesrand circuit:

means connecting the winding of said electromagnet in parallel with said control devices is energized.

8., In an automatic system for an engine driving a controllable pitch propeller, the combination of an changing. motor having a pitch increase winding and a pitch decrease winding; power circuits connected to said windings,- a first power rela havnormally open contacts in the uoi r circuit,

for increase winding; a secono v'er relay having normally open contacts in the power circuit for said relay. having norma contacts; a second control relay having open and normally closed contacts; an energizing circuit including the winding of said second power relay, the normally open contacts of said second control relay and, of said first control having a set of normally open contacts; a second energizing circuit including the winding of said." the normally open contacts of said safety relay and the normally open contacts ii rst power relay,

l in series; a third enerng circuit including the winding of said safety relay and the normally closed contacts of said second ntrcl relay in series, and means for energizing said first control. relay in response to excessive engine speed and said secondv control relay in response to insufiicient engine speed.

In speed responsive control system, the combination of a pair of electro-responsive control devices, control element, means mounting saidcontrol element for rotar movement in a single, plane, deflecting means operated by the device controlled for applying to said control element a deflecting torque proportional to the speed of the device controlled, biasing means operably associated with said control element for applying thereto a biasing torque in opposition to said deflecting torque, an actuating circuit controlled by said control element and operatively connected to said control devices to energize one of said devices when said deflecting torque predominates and the other of said devices when said biasing torque predominates, a magnetic element carried by said control element at a point radially removed from the center thereof, a single electromagnet, means mounting said electromagnet entirely outside of the path of movement of said control element and with its axis substantially at right angles to the plane of movement of said control element and aligned substantially with the posi ion occupied by said magnetic element when said biasing and deflecting torques are equal, and an electrical circuit arranged to energize said electromagnet to attract said magnetic element whenever either of said control devices is energized.

10. In a speed responsive control system, the combination of a pair of control relays, a control element, means mounting said control element for rotary movement in a single plane, deflecting means operated by the device controlled for applying to said control element a deflecting torque proportional to the speed of the device controlled,

said control devices to energize. said electromagnet whenever, either of:

constant speed gOVBIIIOI."

electrical pitch.

decrease Winding; a first control. y open and normally closed normallythe normally closed contacts relay in series; a safety relay biasing" means operably associated with said control element for applying thereto a biasing torque in opposition to said deflecting torque, an actuating circuit controlled by said control element and operatively connected to said relays to actuate one of said relays when said deflecting torque predominates and the other of said relays when said biasing torque predominates, a pair of equal resistances connected in series between the actuating coils of said relays, a magnetic element carried by said control element at a point radially removed from the center of rotation thereof, a single electromagnet, means mounting said electromagnet entirely outside of the path of movement of said control element and substantially aligned with the position occupied by said magnetic element when said deflecting and biasing torques are equal, and an actuating circuit for said electromagnet connecting said electromagnet in parallel with said relays through said resistances, whereby said electromagnet is energized to attract said magnetic element whenever either of said relays is actuated.

11. In an automatic constant speed governor for an engine driving a controllable pitch propeller, the combination of an electrical pitch changing motor having a pitch increase and a pitch decrease winding; a first circuit for energizing said increase winding; a first control relay having normally open contacts in said first circuit and arranged to complete said circuit only when said relay is energized; a second circuit for energizing said decrease winding; a second control relay having normally open contacts in said second circuit and arranged to complete said second circuit only when said relay i energized; a pair of photoelectric cells; light means; electrical means for selectively actuating control relays in response to activation of said cells by light from said light means; a rotatable control element; a light vane carried by said control element and interposed between said light means and said cells, rotation of said control element in one direction moving said vane to allow light to impinge 'upon one of said cells and rotation of said control element in the opposite direction moving said vane to allow light to impinge upon the other of said cells; means for applying to said control element a defiecting torque responsive to tru engine speed;

manually adjustable means operatively connected to said control element to apply thereto a biasing torque in opposition to said deflecting torque and proportional to desired engine speed; electromagnetic restoring means actuated only upon actuation of either of said control relays for restoring said control element to centered position, in which said light vane prevents passage of light from said light means to either of said cells, when the deviation of said control element from centered position is less than a predetermined amount; and electrical safety means for preventing completion of either of said circuits when both of said control relays are simultaneously...

actuated.

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